Virology — MCQs
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Subacute sclerosing panencephalitis (SSPE) is a complication of which viral infection?
Which of the following is NOT a cultivable virus?
What is the descending order of types of viruses causing paralytic polio?
Which of the following viruses can cause infective diarrhoea?
Which feature is characteristic of the virus causing Infectious Mononucleosis?
Which of the following conditions is NOT caused by Parvovirus B19?
Which of the following is a double-stranded RNA virus?
Which of the following is NOT a diagnostic test for chickenpox?
Which of the following is not a prion-associated disease?
Causative agent of molluscum contagiosum is a:
Virology Indian Medical PG Practice Questions and MCQs
Question 131: Subacute sclerosing panencephalitis (SSPE) is a complication of which viral infection?
- A. Mumps
- B. Diphtheria
- C. Measles (Correct Answer)
- D. Pertussis
Explanation: **Explanation:** **Subacute Sclerosing Panencephalitis (SSPE)** is a rare, progressive, and fatal neurodegenerative disease caused by a persistent infection with a **defective Measles virus**. **Why Measles is Correct:** SSPE occurs years (typically 5–10 years) after an initial measles infection. It is caused by a mutant strain of the measles virus that lacks the **M (Matrix) protein**, which is essential for viral budding. Because the virus cannot bud off the host cell, it remains "trapped" within the neurons, spreading directly from cell to cell. This leads to chronic inflammation, demyelination, and neuronal loss in both the gray and white matter (panencephalitis). **Why Other Options are Incorrect:** * **Mumps:** While Mumps can cause acute viral meningitis or encephalitis, it is not associated with a chronic, progressive panencephalitis like SSPE. * **Diphtheria:** This is a bacterial infection caused by *Corynebacterium diphtheriae*. Its neurological complications are due to an exotoxin causing peripheral demyelination (polyneuropathy), not a persistent CNS viral infection. * **Pertussis:** Caused by *Bordetella pertussis*, this bacterial infection can lead to "Pertussis encephalopathy" due to hypoxia or toxins during coughing paroxysms, but it is not a slow viral disease. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Characterized by high titers of anti-measles antibodies in the CSF and serum (**Oligoclonal bands**). * **EEG Finding:** Periodic, high-voltage, slow-wave complexes (Radermecker complexes). * **Histology:** Cowdry Type A intranuclear inclusion bodies in neurons and glial cells. * **Clinical Stages:** Starts with behavioral changes, followed by **myoclonic jerks**, and eventually leads to dementia and vegetative state.
Question 132: Which of the following is NOT a cultivable virus?
- A. Rotavirus (Correct Answer)
- B. Enterovirus
- C. ECHO virus
- D. Coxsackie virus
Explanation: **Explanation:** The correct answer is **Rotavirus**. In the context of standard diagnostic virology and routine laboratory culture, Rotavirus is notoriously difficult to grow. **1. Why Rotavirus is the correct answer:** While Rotavirus can be grown in specialized research settings using specific cell lines (like MA104) and the addition of proteolytic enzymes (trypsin) to enhance infectivity, it is considered **non-cultivable** for routine diagnostic purposes. Diagnosis is primarily achieved through the detection of viral antigens in stool via ELISA or Latex Agglutination, or by visualizing the characteristic "wheel-like" morphology under Electron Microscopy. **2. Analysis of Incorrect Options:** * **Enterovirus, ECHO virus, and Coxsackie virus:** These are all members of the *Picornaviridae* family. Most viruses in this group are readily cultivable in standard human or monkey cell lines (e.g., PMK, human embryonic lung fibroblasts). They typically produce rapid and characteristic Cytopathic Effects (CPE), making culture a viable (though increasingly replaced by PCR) diagnostic method. **3. NEET-PG High-Yield Clinical Pearls:** * **Morphology:** Rotavirus belongs to the *Reoviridae* family; it is a dsRNA virus with a double-layered icosahedral capsid, giving it a "spoked-wheel" appearance. * **Epidemiology:** It is the most common cause of severe dehydrating diarrhea in children worldwide. * **Other "Non-cultivable" Viruses:** For the NEET-PG, remember that **Hepatitis viruses (A, B, C)** and **Norovirus** are also traditionally difficult or impossible to grow in routine cell cultures. * **Vaccines:** Rotavirus vaccines (Rotarix, RotaTeq) are live-attenuated oral vaccines and are part of the Universal Immunization Programme (UIP) in India.
Question 133: What is the descending order of types of viruses causing paralytic polio?
- A. Type 1, type 2, type 3
- B. Type 2, type 1, type 3
- C. Type 1, type 3, type 2 (Correct Answer)
- D. Type 2, type 3, type 1
Explanation: **Explanation:** The Poliovirus belongs to the *Enterovirus* genus and exists in three distinct serotypes: 1, 2, and 3. The correct descending order of their ability to cause paralytic disease is **Type 1 > Type 3 > Type 2**. 1. **Type 1 (Brunhilde):** This is the most common serotype and is responsible for the majority of paralytic poliomyelitis cases and large-scale epidemics. It possesses the highest neurovirulence. 2. **Type 3 (Leon):** This is the second most common cause of paralytic polio. 3. **Type 2 (Lansing):** This type is the least frequent cause of paralysis. Notably, Wild Poliovirus Type 2 (WPV2) was the first to be declared eradicated globally by the WHO in 2015. **Analysis of Incorrect Options:** * **Option A & B:** These are incorrect because Type 2 is the least common cause of paralysis, not the second or most common. * **Option D:** This incorrectly places Type 2 as the most common cause. **High-Yield Clinical Pearls for NEET-PG:** * **Eradication Status:** Wild Poliovirus Type 2 (WPV2) was eradicated in 2015; Type 3 (WPV3) was declared eradicated in 2019. Currently, only **Wild Poliovirus Type 1** remains endemic (primarily in Afghanistan and Pakistan). * **VAPP & VDPV:** While Type 2 wild virus is eradicated, it is the most common cause of **Vaccine-Derived Poliovirus (VDPV)** and **Vaccine-Associated Paralytic Polio (VAPP)** associated with the Oral Polio Vaccine (OPV). * **Switch:** Due to the risk of VDPV2, the Global Polio Eradication Initiative transitioned from Trivalent OPV (tOPV) to **Bivalent OPV (bOPV)**, which contains only types 1 and 3.
Question 134: Which of the following viruses can cause infective diarrhoea?
- A. Rotavirus (Correct Answer)
- B. Calicivirus
- C. Flavivirus
- D. Enterovirus
Explanation: **Explanation:** **Rotavirus** is the most common cause of severe, dehydrating infective diarrhoea in infants and young children worldwide (6 months to 2 years). It belongs to the *Reoviridae* family and possesses a wheel-like appearance under electron microscopy. The primary mechanism of diarrhoea is the destruction of mature enterocytes at the tips of intestinal villi, leading to malabsorption. Additionally, the viral protein **NSP4** acts as an enterotoxin, inducing calcium-dependent chloride secretion, which results in secretory diarrhoea. **Analysis of Incorrect Options:** * **Calicivirus:** While Norovirus (a Calicivirus) is a leading cause of epidemic gastroenteritis in all age groups, Rotavirus remains the classic textbook answer for pediatric infective diarrhoea in the context of this specific question. * **Flavivirus:** This family includes viruses like Dengue, Yellow Fever, and Hepatitis C. They primarily cause systemic febrile illnesses, hemorrhagic fevers, or hepatitis, rather than primary infective diarrhoea. * **Enterovirus:** Despite the name, Enteroviruses (like Poliovirus, Coxsackievirus, and Echovirus) typically cause systemic infections (meningitis, myocarditis, rashes) rather than gastroenteritis. They replicate in the gut but are usually asymptomatic there. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Double-stranded RNA (11 segments), non-enveloped, icosahedral with a double-layered capsid. * **Diagnosis:** Antigen detection in stool via **ELISA** or Latex Agglutination is the gold standard. * **Vaccines:** Live attenuated oral vaccines (Rotarix, RotaTeq, and the indigenous **Rotavac**) are part of the Universal Immunization Programme (UIP) in India. * **Seasonality:** Peak incidence occurs during winter months ("Winter Diarrhoea").
Question 135: Which feature is characteristic of the virus causing Infectious Mononucleosis?
- A. Double-stranded, enveloped DNA virus (Correct Answer)
- B. Double-stranded, non-enveloped DNA virus
- C. Single-stranded, enveloped RNA virus
- D. Single-stranded, non-enveloped DNA virus
Explanation: **Explanation:** Infectious Mononucleosis (Glandular Fever) is primarily caused by the **Epstein-Barr Virus (EBV)**, which belongs to the **Herpesviridae** family (specifically, Human Herpesvirus 4). **1. Why Option A is Correct:** All members of the Herpesvirus family, including EBV, share a specific structural morphology: * **Genome:** They contain **linear, double-stranded DNA (dsDNA)**. * **Capsid:** An icosahedral nucleocapsid. * **Envelope:** They are **enveloped** viruses, acquiring their lipid bilayer from the host cell's nuclear membrane. **2. Why Other Options are Incorrect:** * **Option B:** Non-enveloped dsDNA viruses include Adenovirus and Papillomavirus. EBV requires its envelope for host cell entry via the gp350/220 receptor. * **Option C:** This describes viruses like HIV, Influenza, or Paramyxoviruses. While some RNA viruses cause fever and lymphadenopathy, they do not cause classic Infectious Mononucleosis. * **Option D:** This describes Parvovirus B19, which is the only clinically significant single-stranded DNA virus. **3. High-Yield Clinical Pearls for NEET-PG:** * **Target Cells:** EBV infects **B-lymphocytes** via the **CD21 receptor** (CR2). * **Diagnostic Hallmark:** The presence of **Atypical Lymphocytes (Downey Cells)** on a peripheral smear; these are actually activated **CD8+ T-cells** reacting against the infected B-cells. * **Monospot Test:** Detects **Heterophile antibodies** (IgM) that agglutinate sheep or horse RBCs. * **Associated Malignancies:** Burkitt Lymphoma (t8;14), Nasopharyngeal Carcinoma, and Hodgkin Lymphoma. * **Classic Triad:** Fever, Pharyngitis, and Posterior Cervical Lymphadenopathy. Avoid Ampicillin/Amoxicillin as it can trigger a characteristic maculopapular rash.
Question 136: Which of the following conditions is NOT caused by Parvovirus B19?
- A. Roseola infantum (Correct Answer)
- B. Aplastic anemia in sickle cell disease
- C. Fetal hydrops
- D. Collapsing focal segmental glomerulosclerosis (FSGS)
Explanation: **Explanation:** **Parvovirus B19** is a small, single-stranded DNA virus that targets erythroid progenitor cells by binding to the **P-antigen** (globoside). **Why Roseola Infantum is the Correct Answer:** Roseola infantum (also known as Exanthem Subitum or Sixth Disease) is caused by **Human Herpesvirus 6 (HHV-6)**, and occasionally HHV-7. It is clinically characterized by a high fever for 3–5 days, followed by the sudden appearance of a maculopapular rash as the fever subsides. Parvovirus B19, conversely, causes **Erythema Infectiosum (Fifth Disease)**, famous for the "slapped-cheek" appearance. **Analysis of Incorrect Options:** * **Aplastic Anemia:** Parvovirus B19 infects and lyses red blood cell precursors. In patients with high RBC turnover (e.g., **Sickle Cell Disease**, Hereditary Spherocytosis), this leads to a life-threatening **Transient Aplastic Crisis**. * **Fetal Hydrops:** If a non-immune pregnant woman is infected, the virus crosses the placenta, attacks fetal erythroid cells, and causes severe anemia. This leads to high-output cardiac failure, generalized edema (**Hydrops Fetalis**), and potential fetal death. * **Collapsing FSGS:** Parvovirus B19 is a well-recognized cause of the collapsing variant of Focal Segmental Glomerulosclerosis, particularly in immunocompromised patients, due to direct infection of visceral epithelial cells (podocytes). **NEET-PG High-Yield Pearls:** * **Receptor:** P-antigen (Globoside) found on RBCs and endothelium. * **Arthropathy:** In adults, Parvovirus B19 often presents as acute symmetrical polyarthritis mimicking Rheumatoid Arthritis. * **Pure Red Cell Aplasia:** Seen in immunocompromised patients (e.g., HIV) due to chronic Parvovirus B19 infection. * **Diagnosis:** Detection of IgM antibodies or PCR (especially in aplastic crisis where antibody response may be delayed).
Question 137: Which of the following is a double-stranded RNA virus?
- A. Rotavirus (Correct Answer)
- B. Measles virus
- C. Mumps virus
- D. Influenza virus
Explanation: **Explanation:** The correct answer is **Rotavirus**. In virology, most RNA viruses possess a single-stranded (ssRNA) genome. However, the **Reoviridae** family is the notable exception, characterized by a **segmented, double-stranded RNA (dsRNA)** genome. Rotavirus, a member of this family, contains 11 segments of dsRNA. This segmented nature is crucial as it allows for genetic reassortment, contributing to viral diversity. **Analysis of Incorrect Options:** * **Measles and Mumps viruses:** Both belong to the **Paramyxoviridae** family. They possess a non-segmented, linear, negative-sense single-stranded RNA (-ssRNA) genome. * **Influenza virus:** A member of the **Orthomyxoviridae** family. While it has a segmented genome (8 segments), it consists of negative-sense single-stranded RNA (-ssRNA), not double-stranded. **High-Yield Clinical Pearls for NEET-PG:** * **Rotavirus:** The most common cause of severe, dehydrating diarrhea in children worldwide ("Winter diarrhea"). It infects mature enterocytes of the villi, leading to malabsorption. * **NSP4 Protein:** Rotavirus produces a viral enterotoxin called NSP4, which induces secretion by increasing intracellular calcium—a frequent "image-based" or "fact-based" question. * **Wheel-like Appearance:** The name "Rota" is derived from the Latin word for wheel, referring to its characteristic appearance under electron microscopy. * **Vaccines:** Rotavirus vaccines (Rotarix, RotaTeq, Rotavac) are live-attenuated oral vaccines.
Question 138: Which of the following is NOT a diagnostic test for chickenpox?
- A. FAMA (Fluorescent Antibody to Membrane Antigen) (Correct Answer)
- B. ELISA (Enzyme-Linked Immunosorbent Assay)
- C. Immunofluorescence
- D. PCR (Polymerase Chain Reaction)
Explanation: ### Explanation The correct answer is **A. FAMA (Fluorescent Antibody to Membrane Antigen)**. **Why FAMA is the correct answer:** While FAMA is highly sensitive and specific, it is considered the **gold standard for determining immunity** (serostatus) to Varicella-Zoster Virus (VZV), rather than a routine diagnostic test for active chickenpox. In the context of NEET-PG, diagnostic tests aim to identify the virus or its components during an acute infection. FAMA is technically demanding and primarily used in research settings to assess vaccine efficacy or post-vaccination immunity. **Analysis of other options:** * **B. ELISA:** This is a common serological method used to detect IgM antibodies (indicating acute infection) or IgG antibodies (indicating past exposure/immunity). * **C. Immunofluorescence:** Direct Fluorescent Antibody (DFA) testing is a rapid diagnostic method that uses labeled antibodies to detect VZV antigens directly from skin lesion scrapings. * **D. PCR:** This is currently the **test of choice** for diagnosing chickenpox. It is highly sensitive and can detect VZV DNA in vesicular fluid, crusts, or even oropharyngeal secretions. **Clinical Pearls for NEET-PG:** * **Tzanck Smear:** A classic bedside test showing **multinucleated giant cells** with Cowdry Type A intranuclear inclusions (seen in both VZV and HSV). * **Most sensitive test:** PCR is the gold standard for diagnosing acute infection. * **Gold standard for immunity:** FAMA (as noted above). * **Clinical Presentation:** "Dewdrop on a rose petal" appearance (vesicles on an erythematous base) with lesions in various stages of evolution (pleomorphism).
Question 139: Which of the following is not a prion-associated disease?
- A. Scrapie
- B. Kuru
- C. Creutzfeldt-jakob disease
- D. SSPE (Correct Answer)
Explanation: **Explanation:** The correct answer is **SSPE (Subacute Sclerosing Panencephalitis)**. **Why SSPE is the correct answer:** SSPE is not a prion disease; it is a chronic, progressive neurodegenerative disorder caused by a **persistent infection with a mutant strain of the Measles virus**. It typically occurs years after an initial measles infection due to defective viral replication in the brain. Unlike prions, which are infectious proteins lacking nucleic acids, SSPE is caused by a conventional (though mutated) RNA virus. **Analysis of incorrect options (Prion Diseases):** Prion diseases (Transmissible Spongiform Encephalopathies) are caused by the accumulation of misfolded proteins ($PrP^{Sc}$). * **Scrapie:** This is the prototypical prion disease affecting **sheep and goats**, characterized by intense itching and neurodegeneration. * **Kuru:** Historically found in the Fore tribe of Papua New Guinea, it was transmitted through **ritualistic cannibalism**. * **Creutzfeldt-Jakob Disease (CJD):** The most common human prion disease. It presents as rapidly progressive dementia with myoclonus and characteristic periodic sharp-wave complexes on EEG. **NEET-PG High-Yield Pearls:** * **Prion Characteristics:** Resistant to standard sterilization (autoclaving at 121°C). They require **134°C for 1 hour** or immersion in **1N NaOH**. * **SSPE Diagnosis:** Look for high titers of anti-measles antibodies in the CSF (**intrathecal synthesis**) and "burst-suppression" patterns on EEG. * **Histopathology:** Prion diseases show **spongiform vacuolation** without inflammation. SSPE shows **Cowdry type A** intranuclear inclusion bodies.
Question 140: Causative agent of molluscum contagiosum is a:
- A. Bacteria
- B. Virus (Correct Answer)
- C. Prion
- D. Fungus
Explanation: **Explanation:** **Molluscum contagiosum** is a common viral skin infection caused by the **Molluscum Contagiosum Virus (MCV)**. MCV is a member of the **Poxviridae** family (specifically the genus *Molluscipoxvirus*). It is a large, enveloped, double-stranded DNA virus that replicates exclusively in the cytoplasm of keratinocytes. * **Why Option B is Correct:** The disease is characterized by small, firm, umbilicated papules. The viral nature is confirmed by its structure and the presence of **Henderson-Paterson bodies** (large intracytoplasmic inclusion bodies) seen on histopathology. * **Why Options A, C, and D are Incorrect:** * **Bacteria:** Bacterial skin infections (like Impetigo) typically present with crusting, pus, or cellulitis and respond to antibiotics. * **Prions:** These are misfolded proteins causing neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease), not cutaneous papules. * **Fungus:** Fungal infections (Dermatophytoses) usually present as scaly, itchy patches (Tinea) rather than discrete umbilicated nodules. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** "Pearly, flesh-colored, dome-shaped papules with **central umbilication**." * **Transmission:** Spread via direct skin-to-skin contact, fomites (towels), or sexual contact. * **Histopathology:** Pathognomonic **Henderson-Paterson bodies** (eosinophilic cytoplasmic inclusions). * **Clinical Context:** In adults, extensive lesions or involvement of the face should raise suspicion for **HIV/Immunosuppression**. * **Poxvirus Fact:** It is the largest DNA virus and, unlike most DNA viruses, it replicates in the **cytoplasm** because it carries its own DNA-dependent RNA polymerase.
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Virus Structure and Classification
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Viral Replication
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Pathogenesis of Viral Infections
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DNA Viruses: Herpesviruses
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DNA Viruses: Poxviruses and Adenoviruses
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Hepatitis Viruses
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RNA Viruses: Orthomyxoviruses
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RNA Viruses: Paramyxoviruses
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Enteroviruses and Rhinoviruses
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Arboviruses
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HIV and Retroviruses
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Oncogenic Viruses
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